Police in Sasebo, Nagasaki Prefecture, said Sunday they have arrested a 16-year-old high school girl on suspicion of killing a classmate.

According to police, the victim, Aiwa Matsuo, 15, was visiting the suspect at her apartment when the incident occurred at around 8 p.m. Saturday. TBS quoted police as saying the suspect struck Matsuo on the back of the head more than 10 times with a blunt instrument and strangled her as well. Police said Matsuo’s head had been severed with a large knife and her left hand cut off.

At around 11 p.m., Matsuo’s parents contacted police after their daughter failed to return home. She had told them earlier that she was going to her friend’s place and texted them at about 7 p.m. to say she was about to leave for home.

Police found Matsuo’s body early Sunday morning, lying on the suspect’s bed.

The suspect, who cannot be named because she is a minor, was alone with her classmate at the time of the crime. Police said she does not live with her parents.

The suspect admitted to the crime, police said, but has so far given no motive for the attack.